FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: TomP on February 04, 2021, 07:54:38 PM
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I am trying to use up some of the parts i've got hanging around. So today i just picked up the crank from the machine shop. I had a 390 crank that spun a bearing. I figured some day i'd use it in a 390 with the 351M rods and 410 pistons but have a set of 4.28 bore pistons with a 1.14" compression distance and a 64 top oiler block bored to fit them. Hmmm. So i calculated it out. A 7.1" long rod is the longest normally available and with a 2.20" journal there should be plenty of space to offset that crank to a 3.84" stroke and make a zero deck with those pistons. I could have used a longer stroke but then rods would be a custom size. This saves an otherwise useless crank and pistons.
(https://i.postimg.cc/8zwSzCB7/IMG-9508.jpg)
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What would that be in cubic inches
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4.28 x 4.28 x 3.84 x 6.2832 = 441.977 cubic inches. 1.848958 rod ratio. Should be a quick revving combination. Joe-JDC
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I looked at leaving the stroke standard but offsetting the pin bushings to make the rods 7.13" but this seems easier and didn't cost much more than a regular crank grind. The pin bushings still need to be done as the pistons use a .985" early Hemi pin.
Apparently those long rods are mostly used on 440 Mopar strokers.
This is getting ported C4AE-G heads and an Edelbrock F427 intake so it's not some max effort deal. Mostly using up the parts i've accumulated before I die.
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Cool.. cant wait to see the results :-)
Ricky.
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I use 6.800-7.100" rods on some short stroke FE's. It's the only way to keep the piston weight down with a tall deck block.
This engine used some 7.000" K1's:
http://fepower.net/simplemachinesforum/index.php?topic=9078.0
It was a 4.350" x 3.780" combination, using a custom Superlight Scat crankshaft.
https://www.youtube.com/watch?v=mQ3tRJdDwFQ
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Sounds awesome, but before you buy any parts, but look close at oil feeds on the rod throws when you cut a stock crank that much.
The longer throw of the 390 crank likely makes the oil feed more steep (and better for this) but Brent can certainly chime in with experience on what happens when the crank doesn't want a 2.20 journal
Also, you need to go wider too, not just smaller. Sorry if I am pushing out info you know already, but I haven't gone this way with factory cranks due to cost of fitting the rods
If it works though, should be a fun machine
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Sounds awesome, but before you buy any parts, but look close at oil feeds on the rod throws when you cut a stock crank that much.
The longer throw of the 390 crank likely makes the oil feed more steep (and better for this) but Brent can certainly chime in with experience on what happens when the crank doesn't want a 2.20 journal
Also, you need to go wider too, not just smaller. Sorry if I am pushing out info you know already, but I haven't gone this way with factory cranks due to cost of fitting the rods
If it works though, should be a fun machine
He should be ok on the oil hole location because he's offset grinding. Cutting the width down is always a booger though.
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Sounds awesome, but before you buy any parts, but look close at oil feeds on the rod throws when you cut a stock crank that much.
The longer throw of the 390 crank likely makes the oil feed more steep (and better for this) but Brent can certainly chime in with experience on what happens when the crank doesn't want a 2.20 journal
Also, you need to go wider too, not just smaller. Sorry if I am pushing out info you know already, but I haven't gone this way with factory cranks due to cost of fitting the rods
If it works though, should be a fun machine
He should be ok on the oil hole location because he's offset grinding. Cutting the width down is always a booger though.
8)
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Sounds awesome, but before you buy any parts, but look close at oil feeds on the rod throws when you cut a stock crank that much.
The longer throw of the 390 crank likely makes the oil feed more steep (and better for this) but Brent can certainly chime in with experience on what happens when the crank doesn't want a 2.20 journal
Also, you need to go wider too, not just smaller. Sorry if I am pushing out info you know already, but I haven't gone this way with factory cranks due to cost of fitting the rods
If it works though, should be a fun machine
pic of oil feed holes on my 3.99 stroke crank 2.20 journal and 1.900 width (wasn't a problem on mine, still for sale btw)
He should be ok on the oil hole location because he's offset grinding. Cutting the width down is always a booger though.
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Sounds awesome, but before you buy any parts, but look close at oil feeds on the rod throws when you cut a stock crank that much.
The longer throw of the 390 crank likely makes the oil feed more steep (and better for this) but Brent can certainly chime in with experience on what happens when the crank doesn't want a 2.20 journal
Also, you need to go wider too, not just smaller. Sorry if I am pushing out info you know already, but I haven't gone this way with factory cranks due to cost of fitting the rods
If it works though, should be a fun machine
pic of oil feed holes on my 3.99 stroke crank 2.20 journal and 1.900 width (wasn't a problem on mine, still for sale btw)
He should be ok on the oil hole location because he's offset grinding. Cutting the width down is always a booger though.
Big difference between a steel crank and a cast crank. If you offset grind, it's one thing, but if you cut the journals down to 2.200" and keep it standard stroke, the oil holes on a cast crank can move right into the journal radius.
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The holes did move outward but shouldn't be a problem, he did a nice job radiusing the oil holes toward the center. They are not widened so i'll have to get the rods narrowed.
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Sounds awesome, but before you buy any parts, but look close at oil feeds on the rod throws when you cut a stock crank that much.
The longer throw of the 390 crank likely makes the oil feed more steep (and better for this) but Brent can certainly chime in with experience on what happens when the crank doesn't want a 2.20 journal
Also, you need to go wider too, not just smaller. Sorry if I am pushing out info you know already, but I haven't gone this way with factory cranks due to cost of fitting the rods
If it works though, should be a fun machine
pic of oil feed holes on my 3.99 stroke crank 2.20 journal and 1.900 width (wasn't a problem on mine, still for sale btw)
He should be ok on the oil hole location because he's offset grinding. Cutting the width down is always a booger though.
Big difference between a steel crank and a cast crank. If you offset grind, it's one thing, but if you cut the journals down to 2.200" and keep it standard stroke, the oil holes on a cast crank can move right into the journal radius.
Okay, I wasn't following the reason to reduce the journal without offset grinding. Since it needs new BBC rods anyway gaining stroke seems like an easy thing to do.
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The holes did move outward but shouldn't be a problem, he did a nice job radiusing the oil holes toward the center. They are not widened so i'll have to get the rods narrowed.
I've seen it be a craps shoot there. I had a 352 crank cut down to BBC journals and one oil hole ended up in the fillet. Grinder didn't catch it.
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Yes, it is just common since that the oil hole will move in the direction of the angle that it is drilled at if, the radius of the journal is reduced, w/o offsetting the center line to make up for it. Offset grinding has been around, at least 100 years but, it's usual purpose is aim at as much stroke increase as possible, there by leaving the outer surface in place, minus the material for clean up and I wouldn't remove more than .020, from that surface. Equivalent to a .040 under bearing and using however much you do take off that surface, to increase the journal radius.
With 2.25 journals you can have a FE rod journal offset ground to 3.96 stoke. It can be done for $250 + shipping, in Reddind CA. That's the price I got 1 year ago.
It doesn't help the OP but, a easy offset grind would be a 414/416 ci engine, using 390 Cad rods (2.25 dia x 7/8 wide x 6.5 long) 3.96 stoke with a 390 crank. Used in combination with a 410, 1.660 CH piston (1.660 + 6.5 + 1.98 = 10.140).
It's a little harder but, you could also do it with a Pontiac, 6.625 long x 2.25 dia rod (but they are a little wider on the big end) and .080 over SBC pistons, 1.56 CH, with bushed small ends (1.56 + 6.625 + 1.98 = 10.165).
Just food for thought.
Edit:
One other combo, I forgot to mention, is using the 317/368 Linc rods (if you could find them), they are also 2.250 journals and 7/8 wide. That would work out this way, 1.98 + 7.065 + 1.125 CH = 10.17. There are all kinds of SBF & SBC pistons, with CH's of 1.09, 1.100, 1.125 and 1.130.
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It is stroked, 3.84. Not max at all, it just needed that to match the pistons and available rod lengths. As it is the rods will need to be narrowed and get smaller pin bushings. I wonder if Scat or whoever would make them that way if asked or if they just come already done an inch wide with a .990 pin hole from China?
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I like it! It's different. I want to see what those short pistons will look like.
pl
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TomP,
You may want to reconsider the 7.100 rod length. The 1.140 compression height gets the top of the rod close to the underside of the piston especially if it needs a dish. The pin will be in the oil ring groove which is NO problem. The rod to stroke is 1.84 which could push peak torque up a few hundred rpm over a 6.8 long rod with a 1.77 rod ratio and 1.440 C/H. Your choice , I'll be interested in the outcome either way.
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It is stroked, 3.84. Not max at all, it just needed that to match the pistons and available rod lengths. As it is the rods will need to be narrowed and get smaller pin bushings. I wonder if Scat or whoever would make them that way if asked or if they just come already done an inch wide with a .990 pin hole from China?
I hope this will work, but be sure you get a set of narrowed bearings first and look, Clevite CB743H is one part number, and see how much you can take off the back side without getting into the bearing, maybe you can avoid the bevel side. You'll need to cut .117-.119, you can of course cut either side, or the bearing too, but it gets more difficult the more adaptation it required, and that's a long way
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Narrowing bearings is not a real problem if you know how. Put the bearings in the rod, tighten the bolts snug, and take a carpet knife with new blade and drag it at a 90* the entire circumference of the bevel on either side. Did it with 302 stroker rods and it works like a champ. Goes against your thinking, but it works. Practice on your old bearings. Joe-JDC
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Narrowing bearings is not a real problem if you know how. Put the bearings in the rod, tighten the bolts snug, and take a carpet knife with new blade and drag it at a 90* the entire circumference of the bevel on either side. Did it with 302 stroker rods and it works like a champ. Goes against your thinking, but it works. Practice on your old bearings. Joe-JDC
When you gotta take a lot off, you can also clamp them to a mandrel that you can chuck up in a lathe, then take a tool and cut them down. You gotta narrow a BBC bearing a whole lot to fit on an FE width journal.
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This is how I do it. This is SBC to SBF.
This just to narrow for 229 Chev bearing. To do the bearings and rod, you just make the spud shorter and chamfer after narrowing.
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Narrowing bearings is not a real problem if you know how. Put the bearings in the rod, tighten the bolts snug, and take a carpet knife with new blade and drag it at a 90* the entire circumference of the bevel on either side. Did it with 302 stroker rods and it works like a champ. Goes against your thinking, but it works. Practice on your old bearings. Joe-JDC
I have used a bearing knife, but just to be clear, this is almost 1/8 of an inch difference from a BBC to an FE. If all done on the inside edge of the rod, the bearing will need to be narrowed with the rod because they almost go to the edge, if done on the chamfer side, a narrow bearing usually has some room before the edge of the chamfer, but it likely depends on how much chamfer is needed for the crank fillet and what the the distance from bearing to the new chamfer is after machining. It's likely undoable with a standard with bearing because it would be hanging into the chamfer with a narrowed rod
Small amount can be cut back, but id the shell hits, the shell hits, my only real point is, it's going to take a little thinking that's all
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Guys at Scat say they only offer the off the shelf rods and not narrower or with alternate pin sizes so that will have to be done locally. I'm pretty sure the pistons were made to clear the rods. I bought them years ago. I think they are meant for an MT half inch stroker crank and 392 Hemi rods which are 6.95" long.
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That picture of the arm breaker 6000 , I mean Lathe is a little frightening . 8)
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Tom, I had a conversation about this, about 2 years ago regarding narrowing BBC rods to FE width. Here's the info about that:
Chevs have a .983 wide big end with a .067 offset, Fords have 0. The big ends can be machined to .873, with ~0 offset. Bearing width is .893, I think and the bearings can be machined in the rods and the outside surface chamfered at the same time as the rod, to what ever filet the crank journal has. If you have a lathe large enough to swing the rod, you can do that in 2-3 hours.
You would take the short side of the bearing (inside surface) down to .005/.010 clearance to the bearings edge, on all 8, then turn the rod around and face it to .873. Then chamfer the bearing, after that.
It's not to hard but, you need to know what your doing with the lathe. I can walk you through it, step by step, if you want to do it yourself or give these instructions to a machine shop, with the above picture and they shouldn't have any trouble doing it for you.
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I don't have a lathe or milling machine... though i think i need both... so i'll be at the mercy of whatever machine shop. Sure would be nice if the rods were available that way.
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I agree but, there are no bearings, that I'm aware of, that are 2.2 and will fit a 7/8 wide rod.
There is no demand but, I think a better way to go, is 2.250 journal rods. Lots of 7/8 bearings available for them.
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Yeah but then finding rods for that would become the issue. The crank is already done, though i could save that for something else. The main point of the exercise is to use up these new 1.14" height JE pistons. Using stock 392 Hemi rods would work, they are 6.95" long but the issue there is a rod journal too big to go on any available aftermarket FE cranks.
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CB743H are .835 wide, only leaves you .035 for the chamfer, but could be workable
Edited for typo
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Ross, are those bearings for large chamfer, "H" BBC journals?
If so, they would fit the tangs and you would only need to chamfer them in the rod, while narrowing it.
If not, the tangs could prove problematic. I've never done it but, it is sad that you don't need the tangs but, that's makes for, another machining operation.
In general, 7/8 wide rods, need bearings no wider than 3/4.
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Yes, the CB743H is the narrow BBC, had a typo on my phone but that was an actual measurement
How much you had to massage the bearing would depend on the crank and how much you were able to take off the inside of the rods
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I will check into those bearings. Is that what is normally used on an FE stroker do those cranks have wider journals?
I mocked up the pistons and crank in the block today. I don't have the 7.1" rods yet (just ordered them from Scat) but with a 6.7" Scat rod it sits just around .400 down. Not exact since the .985" pin is loose in the .990 pin hole but a couple thou deck clearance is not an issue.
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I use those Clevites or ACL on strokers. Speedpro also makes a narrow bearing
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The position of the bearings, when install in the rod, will tell you how much you need to take of of the inside surface (rod to rod). Measure that first. You can take that down to .005. The the rest will need to be taken from the outside surface. You will need to know, from the manufacturer or measure the filet radius. Then the chamfer has to be, more than the filet radius, or there will be metal to metal contact, in that area.
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Here are some real pics. I stuck an H mockup bearing I have in a SCAT BBC H-beam. Bearing is .835, you need to get rod down to .870
Very little to no room to cut on the inside. Approx .060 to play on the chamfer side. You need to cut closer to .110.
I think that even if you eat up the extra on the chamfer side, and reduce the chamfer depth itself to a minimum, you'll still be into the bearing on one side or the other
I would love if it would work, and you likely could wack the other .050 or so off the inside of every rod and bearing, but seems like a lot of work for not much gain
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Ross, it looks to me like he has the work in his crank to save, $650 on a crank and $700 or more to save on pistons. I'd say that comes close to $1700. Plus he gets to use the parts he has in the manor he wants.
I get a lot of satisfaction out of doing things like that myself.
Regarding the machine work, that needs to be done. It is rudimentary and can be done at any general machine shop. I would say that the work would take about 3 hours (that's what I would quote, for a job like this) but, to be successful, you have to know the width of the journal and the filet radius.
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Frank, the decision is not mine to judge. However if he could find someone like you to do it, maybe it would be worth it.
I would advise against trying to force it based on having parts, but if you can find a willing machinist, it does look like fun
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Tom
How high an rpm are ya looking at an how much does a 7.1 rod weigh if I may ask ??
I might have missed how much the pistons weighed
No access to machine shop tools anymore or I would do for free
I get real interested in builds such as yours
Ricky.
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I don't even see the weight listed for the 7.1 rods. I'd imagine in the LeMans rod territory. The pistons are light to make up for them. It probably won't see high RPM anyways, it's for a street car, but 7000 is plenty safe.
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Got pic's of the pistons, Tom?
pl
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Good news on the rods, they will sell me ones with unfinished pin bushing that come .969" ID so that saves changing them. Not in stock so he says around three weeks. Just need to be narrowed and i'm sure the local machine shop can handle that. Maybe i could even buy the equpment to do it mysef by then.
Pictures of pistons, and the crank.
(https://i.postimg.cc/t7HdcTZK/IMG-9531.jpg) (https://postimg.cc/t7HdcTZK)
(https://i.postimg.cc/CdHCpgbz/IMG-9532.jpg) (https://postimg.cc/CdHCpgbz)
(https://i.postimg.cc/Yhr6psx8/IMG-9533.jpg) (https://postimg.cc/Yhr6psx8)
(https://i.postimg.cc/8jZhsmKG/IMG-9534.jpg) (https://postimg.cc/8jZhsmKG)
(https://i.postimg.cc/5Xj8zQTC/IMG-9537.jpg) (https://postimg.cc/5Xj8zQTC)
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As you can maybe see the pistons use pin buttons instead of clips. They also come with a raw dome and since i don't really want a 17 to 1 compression ratio those will be cut down to a flat top. The oil holes in the road journals didn't migrate out too far.
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Cool pistons! I'll bet they'll end up pretty light.
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I had a 93 inch Harley shovel head in the early 90’s that made 158 hp that used Teflon buttons instead of a clip , they worked great back then